1. Field of the Invention
The present invention relates to a magnetic recording disk and a process for the manufacture thereof. More specifically, the present invention relates to a magnetic recording disk which has a highly adhesive lubricant layer having so that it not only permits a stable operation without any difficulty at an extremely low level of flying height, for example, of 12 nm or less but also prevents migration even at a high-speed rotation, for example, of 5,400 rpm or more and which is to be mounted on a magnetic recording disk unit such as a hard disk drive unit (HDD), and a process for manufacture thereof.
2. Statement of Related Art
Conventionally, a magnetic recording disk unit employs a CSS (Contact Start and Stop) method in which a magnetic head is kept in contact with a contact start and stop region (CSS region) formed in an inner-circumferential region at a stop time, the magnetic head is allowed to come up slightly at a starting time while it was allowed to contact-slide in the CSS region, and writing and reading are performed in the surface of a write-read disk region formed outside the CSS region. When the operation is ended, the magnetic head is brought back to the CSS region from the write-read disk region and then allowed to land while it was allowed to contact-slide in the CSS region, and the magnetic head is stopped. The starting operation and ending operation which involve the contact-sliding in the above CSS method will be called a CSS operation.
In a magnetic recording disk for use in the above CSS method, it is required to form both a CSS region and a write-read region on the disk surface. For preventing the attachment (stiction) of the magnetic head and the magnetic recording disk when they are in contact, further, it is required to form a roughened form having a predetermined surface roughness called a texture on the magnetic recording disk surface. For alleviating damage caused by the contact-sliding of the magnetic head and the magnetic recording disk during the CSS operation, there are known, for example, a magnetic recording medium (e.g., JP-A-62-66417) having a coating formed of a perfluoroalkylpolyether having the structural formula,HOCH2—CF2O—(C2F4O)p—(CF2O)q—CH2OHand a lubricant containing a phosphazene compound as a main component and being to be applied to a hard magnetic recording disk (e.g., JP-A-11-224419).
Recently, the above CSS method is being replaced with a magnetic recording disk according to a load unload method. The load unload method will be called “LUL method” hereinafter. In the LUL method, a magnetic head is kept on a sloping seat called a ramp positioned outside a magnetic recording disk at a stop time, and at a starting time, the magnetic head is allowed to slide from the above ramp onto the magnetic recording disk after the magnetic recording disk starts turning, followed by writing and reading. The above series of operations will be called “LUL operation”. The LUL method is preferred for increasing the information capacity since a wider writing and reading region on the magnetic recording disk can be secured. Further, since it is not required to form the texture for CSS on the magnetic recording disk surface, the magnetic recording disk surface can be smoothened to a great extent, and the flying height of the magnetic head can be further decreased, so that a higher S/N ratio of recording signals can be attained. The LUL method is therefore suitable.
As the flying height of the magnetic head is further decreasing due to the introduction of the above LUL method, it is required to attain stable operation of the magnetic head even at an extremely low level of a flying height of 12 nm or less. However, when the magnetic head is allowed to fly above a magnetic recording disk surface at such a very low flying height level, there is caused a problem that fly sticking and head corrosion problems frequently take place.
The fly sticking problem refers to a problem that a magnetic head is caused to have a fluctuation in flying position and a flying height level during its flying. The problem involves irregular fluctuations in reproduction output, and a magnetic head comes into contact with a magnetic recording disk to cause a head clash in some cases, and the magnetic recording disk may be destroyed.
The corrosion problem refers to a problem that the element portion of a magnetic head is corroded to cause difficulties in reproducing written data, and in some cases, the reproduction may be no longer possible, or the corroded element may expand to cause damage on the magnetic recording disk surface during the flying of the magnetic head.
Further, it is recent practice to increase the turning rate of a magnetic recording disk for enhancing the response of a magnetic recording disk drive unit. Conventionally, the small 2.5-inch magnetic recording disk drive unit suitable for mobile devices has a turning rate of approximately 4,200 rpm, while it is recent practice to turn a magnetic recording disk at a high rate of 5,400 rpm or more for increasing the response capability. When a magnetic recording disk is turned at such a high rate, a lubricant layer moves (migrates) due to a centrifugal force caused by the turning, and there comes to clearly appear a phenomenon in which the lubricant layer comes to have a non-uniform thickness in the magnetic recording disk surface. When the thickness of the lubricant layer increases on the outer-circumferential side of the disk, a fly sticking problem or a head clash problem is liable to take place at the time of LUL. When the thickness of the lubricant layer decreases on the inner-circumferential side of the disk, the lubricity performance decreases, and a head clash problem is liable to take place.
When a conventional lubricant described in JP-A-62-66417 or a conventional lubricant described in JP-A-11-224419 is used, the above problems take place highly frequently, and it is difficult to satisfy the reliability that magnetic recording disks are recently required to have. It is therefore made difficult to attain higher capacity of a magnetic recording disk, a higher S/N ratio and faster response.
Under the circumstances, it is therefore an object of the present invention to provide a magnetic recording disk that permits a stable operation without any hindrance at an extremely low level of flying height, for example, of 12 nm or less, and which has a highly adhesive lubricant layer whose migration can be prevented at a turning rate, for example, of 5,400 rpm or more, and a process for the manufacture thereof. Particularly, the present invention aims at providing a magnetic recording disk suitable for the LUL method and a process for the manufacture thereof.